The earliest reports of flumazenil's antagonist effects at the benzodiazepine receptor did not report significant intrinsic activity. In contrast to these early reports, more recent studies have reported agonist, and even inverse agonist, effects of flumazenil across several measures and species. The purpose of the present study is to characterize the discriminative stimulus and self-reported effects of flumazenil in humans. Six subjects learned to discriminate flumazenil (0.56 mg/70 kg; iv) from saline. In addition, substitution tests with various doses of flumazenil (0, 0.10, 0.32, 0.56 and 1.0 mg/70 kg) demonstrated dose- dependent increases on several self-report measures sensitive to sedative- like effects (e.g., PCAG subscale of the ARCI, sedative rating on the adjective rating scale), as well as increased ratings of "high" and "strength of drug effect". Taken together, these results support other research suggesting agonist effects of flumazenil. Future studies will focus on determining the specificity of flumazenil's agonist effects at the benzodiazepine receptor.